The present invention relates to coating compositions for providing controlled release of pressure sensitive adhesives (PSAs) adhered thereto. More precisely, the present invention relates to moisture-curable silicone compositions which cure rapidly, when they are applied to a substrate and exposed to moisture, and provide a cured coating on the substrate which will release various pressure sensitive adhesives with a pre-selected force.
Rapidly curable coating compositions are required in fast-paced coating operations, such as paper or fiber coating operations, wherein, in rapid succession, a curable composition is applied to a substrate, the applied composition is cured and the coated substrate is subjected to further operations such as packaging, spooling, rolling, cutting or further coating.
Homan has disclosed rapidly curing, moisture-curable coating compositions in U.S. Ser. No. 520,793; entitled "Coating Process and Moisture-Curable Organopolysiloxane Compositions Therefor", which was filed on Aug. 5, 1983 and which is assigned to the assignee of the present invention. The compositions and process of Homan provide a means for coating a substrate, such as paper, with a cured, adhesive-releasing coating in as little as 10 seconds at room temperature. However, there are some instances when the preferred compositions of Homan, which are predominantly polydimethylsiloxane compositions, provide undesirably low release of pressure sensitive adhesives.
For example, in a process for preparing pressure sensitive adhesive labels a laminate of adhesive-bearing label stock and silicone-bearing backing paper is die-cut on its label stock side to provide a plurality of labels surrounded by a waste matrix, both still adhered to the backing paper. The waste matrix is typically rapidly stripped away and discarded, leaving only the die-cut labels adhered to the uncut backing paper. For such a process it is highly desirable that the force required to separate the adhesive from the coating be sufficiently low to allow easy stripping of the waste matrix but sufficiently high to retain the labels on the backing paper during the stripping operation. Typically a release force of from 100 to 200 grams/inch (38.6 to 77.2 N/m) is desired for such a process.
For another example, in the preparation of rolls of pressure sensitive adhesive tape a support material, such as paper or polymeric film, is provided with a cured silicone release coating and a pressure sensitive adhesive coating. The resulting stock is rolled into a roll configuration so that the adhesive coating is adhered to the silicone release coating over substantially its entire surface. In such a product the force required to separate the adhesive from the coating should be sufficiently low to allow the easy unwinding of the roll of tape, when desired, but sufficiently high to retain the tape in the roll configuration during the preparing, storing and handling of the roll. Typically a release force of from 200 to 400 grams/inch (77.2 to 154.4 N/m) is desired for such an article.
The predominantly polydimethylsiloxane-based compositions of Homan typically release styrene-butadiene rubber (hereinafter SBR) pressure sensitive adhesives with a force less than 100 g/in. (38.6 N/m); however, as noted above, a release force of greater than 100 g/in. is frequently needed. There is therefore a need for improved moisture-curable silicone release coatings wherein their adhesive-release forces can be increased when desired.